The present invention relates generally to imaging techniques. More particularly, the invention provides a method and system for generating synthetic panchromatic images. Merely by way of example, the invention has been applied to generating high resolution pan-sharpened multi-spectral images. The method and system for generating high resolution images can be used to generate satellite imagery products. Additionally, it would be recognized that the invention has a much broader range of applicability.
Optical systems have been widely used for detecting color images of various targets. Such optical systems often employ a panchromatic detector and a multi-spectral detector. The panchromatic detector generates panchromatic gray-scale images, while the multi-spectral detector detects spectral images in various bands of wavelengths, such as red, green, blue and near infrared (“NIR”) bands. The panchromatic detector typically possesses a spatial resolution higher than that of the multi-spectral detector. Using the multi-spectral detector with relatively low resolution reduces costs of optical systems and associated transmission bandwidth requirements. Further, the high resolution panchromatic images and the low spatial resolution multi-spectral images can be mathematically combined to form high resolution multi-spectral images in a process called pan-sharpening. A system acquiring and synthesizing the multi-spectral images and the panchromatic images is described below.
FIG. 1 is a simplified diagram for a conventional optical system with panchromatic detector and multi-spectral detector. Optical system 110 is an imaging system positioned in a spacecraft that generates images of targets on the earth surface. Optical system 110 includes at least multi-spectral image detector 120 and panchromatic image detector 130. Multi-spectral detector 120 generates multiple images in different bands of wavelengths. As discussed above, the bands of wavelength may include red, green, blue and NIR bands. Within optical system 110, multi-spectral detector 120 and panchromatic detector 130 are placed in different locations. For each imaging object, optical system 110 generates multiple images, such as panchromatic, red, green, blue and NIR images. The specific processes for image acquisition is described below.
FIG. 2 illustrates a simplified conventional process for optical system 110 to capture multiple images of an imaging target on the earth surface. Optical system 110 moves with respect to earth surface 210. For example, at time t1, panchromatic detector 130 of optical system 110 captures a panchromatic image of imaging area 220. Subsequently, at time t2, multi-spectral detector 120 of optical system 110 captures several spectral images of imaging area 220. In another example, at time t1, multi-spectral detector 120 of optical system 110 captures several spectral images of imaging area 220. Subsequently, at time t2, panchromatic detector 130 of optical system 110 captures a black-and-white image of imaging area 220. The interval between time t1 and time t2 is usually small. For example, the interval may be only 0.5 second. Nonetheless, during this short interval, imaging surface 220 may have changed. Additionally, imaging angle α1 at time t1 and imaging angle α2 at time t2 are usually different. The imaging angle is the angle between the imaging direction and the reference direction vertical to imaging area 220. Consequently, the panchromatic image may not match the multi-spectral images, and this mismatch creates difficulties in producing high resolution color images.
Hence it is desirable to improve technique for creating high resolution color images.